Cross-linked polymer hydrogel materials are widely utilized in the biomedical industry. They are used in contact lenses, blood contact materials, controlled release formulations, wound dressings, bioadhesives, membranes, superabsorbents, cell encapsulation and immunoisolation materials, and tissue engineering scaffolds. Among the different polymers, the naturally occurring polysaccharide alginic acid has found biomedical applications because of its biocompatibility, relative biological inertness, and the ability to engineer its mechanical properties by introducing various types of chemical and physical crosslinks. Alginic acid distinguishes itself from other biologically occurring polysaccharides in its ability to form stiff hydrogels when exposed to cross-linking calcium ions at slightly supraphysiological concentrations. This property has been utilized to devise a treatment for damaged heart tissue of patients at risk for adverse remodeling of the left ventricle of the heart following acute myocardial infarction (AMI). An aqueous soluble formulation of sodium alginate and calcium-D-gluconate, the concentration of each component carefully chosen to achieve partial crosslinking of the alginate molecules, yet providing for a stable free flowing liquid, is injected into the coronary artery of AMI patients after revascularization. The formulation undergoes a transition from liquid to gel when in contact with the infarcted cardiac tissue as a result of the elevated extracellular calcium concentration in the re-perfused cardiac tissue. The hydrogel then deposits in the interstitial tissue and exerts a beneficial therapeutic effect by reducing adverse remodeling and heart failure, potentially because of its mechanical support of the weakened heart wall.
The deposition of this alginate hydrogel in the injured reperfused myocardium of AMI patients is unknown as comprehensive invasive heart tissue sampling in human patients cannot be conducted. Also, the utility of invasive tissue sampling techniques in a preclinical setting is limited because the surgical intervention often constitutes a terminal procedure that prevents longitudinal assessment in the same research subject. Non-invasive imaging techniques can offer a solution by providing this information without surgical intervention or terminal procedures. Imaging modalities such as echocardiography, computed tomography, magnetic resonance imaging, and nuclear imaging such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) use specialized imaging reagents and/or instrumentation to assess heart structure, function, perfusion and remodeling in patients with AMI or heart failure as well as in animal models of these diseases.